Thickness difference induced pore structure variations in cellulosic separators for lithium-ion batteries

摘要

The pore structure of the separator is crucial to the performance of a lithium-battery as it affects the cell resistance. Herein, a straightforward approach to vary the pore structure of Cladophora cellulose (CC) separators is presented. It is demonstrated that the pore size and porosity of the CC separator can be increased merely by decreasing the thickness of the CC separator by using less CC in the manufacturing of the separator. As the pore size and porosity of the CC separator are increased, the mass transport through the separator is increased which decreases the electrolyte resistance in the pores of the separator. This enhances the battery performance, particularly at higher cycling rates, as is demonstrated for LiFePO4/Li half-cells. A specific capacity of around 100 mAh g-1 was hence obtained at a cycling rate of 2 C with a 10 μm thick CC separator while specific capacities of 40 and close to 0 mAh g-1 were obtained for separators with thicknesses of 20 and 40 μm, respectively. As the results also showed that a higher ionic conductivity was obtained for the 10 μm thick CC separator than for the 20 and 40 μm thick CC separators, it is clear that the different pore structure of the separators was an important factor affecting the battery performance in addition to the separator thickness. The present straightforward, yet efficient, strategy for altering the pore structure hence holds significant promise for the manufacturing of separators with improved performance, as well as for fundamental studies of the influence of the properties of the separator on the performance of lithium-ion cells.